German Patent No. 195 00 800 describes a rotational speed sensor having seismic masses in a spring suspension on a substrate so they can be deflected under the effect of acceleration. In addition, the acceleration sensor has analysis devices for detecting acceleration-induced deflection of the seismic masses. For this purpose, the seismic masses are suspended so that deflection by any interfering acceleration, especially linear acceleration, is suppressed. The rotational speed sensor is used to detect Coriolis acceleration in particular.
German Patent No. 44 31 478 describes an acceleration sensor having a seismic mass which is suspended on flexible elements and can be deflected by the action of acceleration. An electrode mounted on the seismic mass is moved relative to a stationary electrode, so the capacitance of the resulting capacitor changes due to acceleration. The change in capacitance is detected by measurement. The sensor is used for detection of linear acceleration.
Finally, an acceleration sensor which is designed as a Coriolis rotational speed sensor is described in German Patent No. 195 23 895 (a later publication). In one embodiment, the Coriolis rotational speed sensor is also designed for detection of linear acceleration. To do so, an additional electronic position controller is assigned to an oscillating structure which is formed by seismic masses and is suspended so that it can move with rotary oscillation, and the position controller detects and damps the linear acceleration acting on the oscillating structure. This electronic position controller is formed by comb structures arranged on the oscillating masses to engage with additional comb structures, so that capacitances between the two comb structures can be measured by applying a voltage. When the oscillating structure is deflected due to linear acceleration, the distance between the individual fingers of the comb structures changes, resulting in a change in capacitance which is detected by the electronic position controller. By changing the voltage applied to the comb structures, it is possible to regulate the distance between the comb structures to a predetermined setpoint using the electrostatic effect. At the same time, the voltage level used for the distance control supplies information regarding the magnitude of the linear acceleration acting on the oscillating structure.
One disadvantage of the acceleration sensor described in German Patent No. 195 00 800 is that linear acceleration cannot be detected because linear acceleration is actually suppressed or attenuated.
Furthermore, the acceleration sensor described in German Patent No. 44 31 478 can detect only linear acceleration. Therefore, it is not suitable when both linear acceleration and Coriolis acceleration are to be detected.
One disadvantage of the Coriolis rotational speed sensor described in German Patent No. 195 23 895, which is supposed to detect linear acceleration at the same time, is that the amplitude of the rotary oscillation is several times greater than the respective perpendicular amplitude of the oscillation of the comb structure of the position controller. The amplitude of the rotary oscillation is on the order of 10 to 30 .mu.m, and the amplitude of the oscillation of the comb structure of the position controller is on the order of 1 nm. Thus, the oscillation of the comb structure is superimposed on the rotary oscillation, so that the signal for the electronic position controller of the comb structure is also influenced by the rotary oscillation. This makes it difficult to use the electronic position controller signal for an accurate determination of linear acceleration. However, for certain applications of acceleration sensors, ability to accurately determine both linear acceleration and non-linear acceleration, e.g., Coriolis acceleration, is required.